A laser printer prints an image based upon image data obtained, for example, by digitizing, i.e., quantizing, an analog image. At such time each scanning line of the image is divided into pixel areas and a laser beam that has been modulated in accordance with each item of pixel data illuminates each pixel area on a photosensitive drum that corresponds to the pixel. The pixel area on the photosensitive drum thus illuminated by the laser beam is converted from an electrically charged state to a discharged state and an electrostatic latent image corresponding to the image data is formed on the photosensitive drum. This electrostatic latent image is visualized by a developing unit and the toner image thereof is transferred to paper to thereby obtain a printed image.
There is strengthening demand for laser printers of improved printing quality and this has been accompanied by the proposal of various techniques. In order to solve the problem of jaggies along diagonal lines, the U.S. Pat. No. 4,847,641 proposes a technique whereby previously stored patterns and a bitmap are compared piece by piece, a compensation dot is generated if there is a match and the dot for which the match was obtained is replaced by the compensation dot. By virtue of this technique, the dots of an edge portion along which jaggies are produced in the original image data are changed to dots (correction dots) of smaller size to thereby partially raise the resolution of the image. As a result, a smooth edge is expressed and an image of higher definition is obtained.
Although a high-definition image is obtained by such a technique, the problem set forth below still arises. By way of example, FIG. 17 illustrates an example in which a two-point very small kanji character “” has been printed at a resolution of 600 dpi×600 dpi. It will be understood that a thickened portion occurs at an intersection of lines in this character. If it is attempted to print a small-point character, e.g., a two-point character (small size character), using a conventional laser printer, there will be instances where an intersection of lines in the character develops such a thickened portion. Since this a thickened portion has a size on the order of about one pixel, it is almost inconspicuous in the case of a character of ordinary size. However, such a thickened portion becomes more conspicuous as character size decreases.